Mix the mirin and shoyu together in a bowl. Place the kumera and tofu in a pan and boil for 10 minutes, add the sprouts and cook for a further 5 minutes. Remove from the heat and drain off any water and blot dry the tofu and kumera. Set the sprouts aside for later
Pour the mirin and shoyu mixture over the tofu and sweet potato and set aside to marinate.
Dry roast the cashews in a pan until they are slightly golden. Remove from the heat and set aside.
Boil the noodles for 3 - 4 minutes until tender.
Cut the sprouts in half.
In a large pan heat ½ the quantity of oil and fry the Brussel sprouts cut side down until golden. Remove the sprouts from the heat and heat the remaining oil. Fry the tofu and sweet potato next reserving the marinade for the noodles.
Toss the remaining marinade over the noodles and serve with the tofu, sprouts and sweet potato. Sprinkle the cashews over each dish and serve.
Note: Buckwheat noodles are made with a combination of buckwheat flour and wheat flour. The best quality noodles use more buckwheat than wheat flour - price often determines quality but double check by looking at the ingredient list - whichever ingredient is first is used in the greatest quantity. They are not suitable for coeliacs.